Relative air speed indicators are utilized where it is desirable or necessary to have a visual indication of air speed with respect to a moving vehicle. In other words, "relative air speed" or "air speed" as used herein means the speed of a vehicle as it passes or moves through a body of air. "Ground speed" is used herein to denote the speed of the vehicle with respect to land or water; and "wind speed" will refer to the speed of air with respect to land or water.
Thus, air that is stationary on land or water will have a zero wind speed. A vehicle moving across the land or water and through a stationary body of air will have a ground speed that is the same as its air speed. If the body of air is moving across the land or earth in the same direction as the vehicle is traveling, then the vehicle's ground speed will be higher than the vehicle's air speed. Hence, relative air speed will be higher or lower than ground speed, depending on the wind speed vector, i.e., the direction and speed of the wind.
Typically, relative air speed indicators are of two types. The first type utilizes a visual indicator mounted on the exterior of the vehicle. Air speed is observed by viewing the visual indicator directly. The second type comprises a sensor on the exterior of the vehicle that communicates with a visual indicator mounted on the interior of the vehicle. This second type of air speed indicator has the disadvantage of requiring extensive modification to install on existing vehicles. Furthermore, this type of indicator is designed to communicate only air speed and has no decorative or ornamental features associated with the indication or display of air speed.